Transferring data associated with various time-critical applications in IP-based networks has been an attractive topic in recent years. It has also been one of the main goals in the development of the mobile communications systems, and especially in so-called third generation mobile communications systems, such as UMTS (Universal Mobile Communications System). A mobile communications system refers generally to any telecommunications system which enables wireless communication when users are moving within the service area of the system. A typical mobile communications system is a Public Land Mobile Network (PLMN).
One UMTS system based on IP technology is the so-called 3GPP AII-IP system, which is defined in the 3rd generation partnership project 3GPP. One standard used for IP telephony implementation in 3GPP AII-IP is SIP. SIP is an application-level control protocol which allows the establishment, alteration and interruption of multimedia connections and voice over IP connections. IP telephony is a general term covering services from standard voice telephony utilizing an IP protocol (VoIP, Voice over IP) to multimedia applications using IP data, voice and video.
In the 3GGP AII-IP system, the intelligent network service implementation may be based on the CAMEL architecture. One of the problems to be solved when implementing CAMEL to the network using SIP, is how to transfer at least mandatory CAMEL-related information used for charging purposes between network nodes/functions using SIP. In the GSM system CAMEL-related information is obtained by sending a routing number request. However, in SIP such mechanism does not exists.
One solution to the above problem is to provide SIP with a routing number request mechanism corresponding to the one used in GSM to transfer CAMEL-related information. A problem with this kind of a solution is -that it would require new messages in SIP.